How to provide a python argparse.parser with arguments from inside the code, without command-line arguments?

Question

I have a code that takes the command-line arguments into a parser and modifies some configuration settings. Something like this:

command:

python mycode.py --config-file "some_file.yaml" SOMETHING.subsetting_a 2 SOMETHING.subsetting_b 3

and then it does:

import argparse
parser = argparse.ArgumentParser(description="Some description here")
parser.add_argument(
    "--config-file",
    default="",
    metavar="FILE",
    help="path to config file",
    type=str,
)
//some more 'add_argument' lines here
args = parser.parse_args()

But as I am using jupyter notebook, it would be easier to provide the arguments directly to the parser, as if they come from the command-line. How can I create a string containing the command (as mentioned above) and pass it to parser?

You can also create a args = argparse.Namespace(config_file='some_file.yaml', ...) (skipping the parse_args step). — hpaulj
– hpaulj, Commented May 30, 2019 at 6:30

ShadowRanger · Accepted Answer · 2019-05-29 23:10:42Z

3

parse_args's first optional argument is the list of arguments to parse, the signature is:

ArgumentParser.parse_args(args=None, namespace=None)

It just takes args from sys.argv if you don't provide it.

So just call it as:

args = parser.parse_args(['mycode.py', '--config-file', "some_file.yaml", 'SOMETHING.subsetting_a', '2', 'SOMETHING.subsetting_a'])

(with the list containing whatever you like instead) and it will use it instead of sys.argv.

answered May 29, 2019 at 23:10

ShadowRanger

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Azim · Accepted Answer · 2019-05-29 23:15:05Z

1

Note: As @ShadowRanger mentioned, there is no need to use sys.argv. See his response.

One way is to use sys.argv to mimic the command-line arguments:

import sys

sys.argv = [
    "--config-file" , "some_file.yaml",
    "SOMETHING.subsetting_a" , "2",
    "SOMETHING.subsetting_b" , "3"]

args = parser.parse_args(sys.argv)

The content of args is something liek this:

> Namespace(config_file='some_file.yaml', opts=['SOMETHING.subsetting_a', '2', 'SOMETHING.subsetting_b', '3')

which is similar to the output of print(parser.parse_args()).

edited May 29, 2019 at 23:15

answered May 29, 2019 at 23:07

Azim

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5 Comments

ShadowRanger Over a year ago

You passed non-existent arguments to parse_args. I think you may have misunderstood the documentation; you could have passed the list directly as an argument to parse_args instead of modifying sys.argv at all.

Azim Over a year ago

That was a typo. Thanks. And yes you are right about not needing sys.argv. I will update it.

hpaulj Over a year ago

The unit test file for argparse tests both a direct list of strings and a doctored sys.argv.

ShadowRanger Over a year ago

@hpaulj: Yar. It's perfectly legal, the reason not to do it is that you shouldn't be using global state to solve a local problem. The contents of sys.argv often mean something, and you shouldn't mess with them willy-nilly if there is any other way to accomplish your aims.

hpaulj Over a year ago

It this case of a jupyter notebook the real sys,argv has already been used by the jupyter server. So modifying it for 'local' use should be fine - though it may affect other notebooks on the same server.

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